A fuel cell converts chemical energy stored in a fuel into a useful form of energy, such as for example, electricity. One example of a particular type of fuel cell is a Proton Exchange Membrane (PEM) fuel cell that is operable to produce electricity.
A typical PEM fuel cell includes an electrolyte membrane arranged between an anode electrode and a cathode electrode. Hydrogen fuel is supplied to the anode electrode and an oxidant is supplied to the cathode electrode. Within the PEM fuel cell the hydrogen fuel and the oxidant are employed as reactants in a set of complementary electrochemical reactions that yield electricity, heat and water.
A number of factors cause other undesired reactions to occur that increase the rate of wear and degradation experienced by some components of a PEM fuel cell. For example, small amounts of hydrogen fuel and oxidant remaining inside a PEM fuel cell, after respective supplies of these reactants are closed off, are known to combust during shutdown and restarting processes. Combustion within a PEM fuel cell causes the deterioration of various components including the electrolyte membrane and catalyst layers deposited on the electrodes. The cumulative deterioration of various components significantly reduces the efficiency of the PEM fuel cell and may lead to failure of the PEM fuel cell.
More specifically, combustion as opposed to electrochemical consumption of the hydrogen and oxygen occurs because the conditions within a PEM fuel cell module start to change as support systems operable during the normal operation (i.e. the “on” state) of the PEM fuel cell module are switched to an “off” state. As the internal conditions change, some hydrogen molecules diffuse to the cathode side of the membrane and burn in the presence of the oxygen. Similarly, some oxygen molecules diffuse across the membrane and react with the hydrogen fuel on the anode side of the membrane. The diffusion of hydrogen across the membrane is actually more common (in the absence of a driving differential pressure across the membrane) since hydrogen molecules are smaller than oxygen molecules, and, thus more readily diffuse through the membrane.
Another undesired reaction that may occur is the electrochemical corrosion of at least one catalyst layer within a PEM fuel cell. This further deteriorates the performance of a PEM fuel cell.